Corrosion inhibitors have been utilized for many years to protect corrosion of metal parts. The corrosion inhibitors are compounds that form an extremely thin film over selected metal surfaces. As corrosion is an electrochemical process, the formation of the thin film of the corrosion inhibitors acts as an electron acceptor and the metal surface, containing an oxide coating, acts as an electron donor. See also, An Overview: Corrosion Inhibitors; Subramaniam, A. et al., Corrosion Vol. 56, No. 2, pages 144–155.
Metals exposed to the environment of an automatic dishwasher endure corrosive conditions such as high electroyte concentration, high humidity, high pH, high temperature, contact with bleach, shear stresses from foreign matter such as soils, different aeration and concentrations based on the shape of the dishware and relatively long and repeated periods of exposure to the discussed elements.
Stainless steel, comprising an alloy of chromium, nickel and steel, is often the alloy of choice for cookware, flatware and other cooking utensils. Carbon steel cooking surfaces and chrome plated cookware and cooking utensils also are prevalent in consumers' kitchens. Many consumers utilize automatic dishwashers to clean cookware, flatware and cooking utensils. However, stainless steel is relatively susceptible to corrosion under the described automatic dishwasher conditions. The properties and corrosion factors of stainless steel are distinct from that of sterling silver and traditional solutions utilized for sterling silver do not prove to be useful for stainless steel. Like sterling silver, tarnishing of stainless steel as well as rusting is often identified as corrosion in stainless steel.
Therefore, there exists a need to provide protection to stainless steel metals in automatic dishwasher conditions while continuing to provide acceptable levels of cleaning and spotting. The corrosion inhibitor must be able to be formulatible in an automatic dishwashing composition comprising such additives as bleach and enzymes as well as be safe to use on dishware.